With current finite linear motion guide units of the sort recited just above, the cage holding rolling elements therein at lengthwise regular intervals is disposed between the guideway members in a way moving over half of a stroke which is the distance the guideway members travel or move past each other in lengthwise direction. In prior finite linear motion guide units, however, the cage used to stray in increments from a desired location it should be relative to the guideway members, dependent on a diversity of working conditions including variations in load carried on the guide unit, processing accuracy of guideway grooves machined on the guideway members, working geometry where the guide unit operates in an upright posture, high traveling velocity, high acceleration/retardation, and so on. To cope with this, most of the finite linear motion guide units have conventionally the cage with means for preventing the cage from straying or wandering. An example of the prior means for preventing the cage from wandering installed in the finite linear motion guide units is composed of a rack-and-pinion arrangement in which the cage has a pinion while the guideway members have racks, respectively, so that the pinion comes into mesh with the rack to keep the cage in place with respect to the guideway members.
A finite linear motion guide unit has been shown before in the commonly assigned Japanese Laid-Open Patent Application No. 2004-197 850. As disclosed in FIGS. 4-6, 8-10 and 14 in the above-cited reference, a pinion holder 6 is inserted into a window 30 in a cage 3 after once getting deformed elastically by itself, and then released from the deforming stress to fit snugly into the window to come into engagement with the cage 3. Next, a pinion shaft 36 is forced into a bearing recess in the pinion holder 6 to carry the pinion 5 for rotation. To retain surely the pinion holder 6 inside the window 30, the pinion holder 6 has a flange 46 extending out of any side 42 of the pinion holder 6 so as to come into abutment against any one surface (for example, the reverse) of an edge 34 around the window 30, and a snap hook 40 extending out of the other side of the pinion holder 6 to come into engagement with another surface (for example, the obverse) of the edge 35 around the window 30.
With the prior finite linear motion guide unit constructed as stated earlier, however, the pinion holder 6 as shown in FIG. 2 has a transverse section wider than a raceway groove 10 of a guideway member 1 or 2 to fill a clearance between wall surfaces 15 and 16 opposite to each other of the guideway members 1 and 2, with the result that the raceway groove 10 of V-shape gets inevitably less in depth. Thus, the raceway area where a raceway surface 11 or 12 comes into rolling contact with a rolling element 8 of cylinder gets less in effective load-carrying width. Consequently, the finite linear motion guide unit could carry only lighter load.
Modern industries are in need of the finite linear motion guide unit having the guideway members more in load-carrying capacity than ever as well as capable of operating under working conditions which expect the guideway members to travel or move past relatively each other with higher acceleration/retardation. To deal with the need as stated earlier, the finite linear motion guide unit of the present invention has the capacity of carrying heavy loads and also has the rack-and-pinion arrangement inexpensive in construction to prevent the cage from straying or wandering lengthwise, thereby keeping the cage in correct place with respect to the guideway members even under high acceleration/retardation. Thus, the finite linear motion guide unit developed according to the present invention is tolerable to higher loads and suitable for working condition of higher acceleration/retardation than in the conventional finite linear motion guide units.